Patients with Alzheimer's disease often complain of inability to find their way even in familiar surroundings. Many such patients suffer deterioration of visual function by the loss of acuity, contrast sensitivity, and visual motion sensitivity. We are testing a large, community-based cohort of Alzheimer's patients to determine whether their difficulties with spatial orientation might be the result of impaired visual motion processing. Our hypothesis is that focal cortical degeneration in extrastriate visual areas creates a specific incapacity to access the orienting cues imbedded in the optic flow field. These subjects and age-matched controls are tested with an extensive battery of neuropsychological instruments and clinical measures of visual function. This provides a database for quantifying the severity and variety of impairments included in the standard diagnostic criteria for Alzheimer's and senile visual dysfunction. We then use optic flow field stimuli to test each subject's capacity to indicate the direction of heading in the simulations and to respond to these stimuli with appropriate postural adjustments. Our goal is to assess the contributions of optic flow field analysis to visuospatial orientation in the elderly to determine if cortical degenerative disease can specifically impair this function and lead to disability.